Origins
The word 'air' entered English around 1300 from Old French 'air,' from Latin 'āēr,' from Greek 'āḗr' (ἀήρ). In early Greek usage, 'āḗr' did not mean the atmosphere in general — it specifically denoted the lower, misty, hazy layer of the atmosphere, as distinct from 'aithḗr' (αἰθήρ, ether), the bright, clear, fiery upper sky where the gods dwelled. This distinction was cosmologically important: 'āḗr' was associated with darkness, fog, and obscurity, while 'aithḗr' was associated with light, purity, and the divine.
The Greek word may derive from the verb 'áein' (ἄειν, to blow) or from a PIE root *h₂weh₁- (to blow, to breathe). The connection to blowing and breathing makes intuitive sense — air is the substance that moves when wind blows and that enters the lungs when we breathe. However, the precise PIE etymology of Greek 'āḗr' remains debated.
Before the adoption of French/Latin 'air,' the native English word was 'lyft' (air, atmosphere, sky), from Proto-Germanic *luftuz, which survives in German 'Luft' (air) and in the compound 'Luftwaffe' (air weapon, the German air force). 'Lyft' was largely displaced by 'air' after the Norman Conquest, following the general pattern of French vocabulary replacing native English terms in educated and literary usage. The Germanic word survives in English only in 'loft' (an upper room, literally 'up in the air') and 'aloft' (high up, in the air).
Latin Roots
The Greek root 'āḗr' gave rise to an enormous family of English scientific and technical terms through the Latin prefix 'aero-': aeronautics (the science of air navigation), aerodynamics (the study of air in motion), aerobics (exercise requiring air/oxygen), aeroplane (air-wanderer, though 'airplane' is now standard in American English), aerosol (a suspension of particles in air), and aerate (to infuse with air).
Italian 'aria' (air), a direct descendant of Latin 'āēr,' entered English as a musical term — an 'aria' is literally 'an air,' a melody. The English expression 'to put on airs' (to behave affectedly) comes from the musical sense: one 'performs' a manner as one performs a tune. The compound 'malaria' — Italian 'mala aria,' bad air — reflects the pre-modern belief that diseases were caused by miasma, noxious vapors rising from swamps and rotting matter. The germ theory of disease disproved this mechanism, but the word persists as a linguistic fossil of an obsolete medical paradigm.
Aristotle classified air as one of the four classical elements, alongside earth, water, and fire. In his system, air was hot and wet, positioned between fire (hot and dry) and water (cold and wet). This four-element theory dominated Western thought for nearly two thousand years until Antoine Lavoisier demonstrated in the 1770s that 'air' was not an element at all but a mixture of gases — primarily nitrogen and oxygen.